CAPE CANAVERAL, Florida (Reuters) - The U.S. company that has arranged for six tourists to fly in space said on Friday it is staying open for business despite the economic crisis and a lack of confirmed flight opportunities.

Space Adventures has been setting up flights aboard Russian Soyuz capsules when there are spare seats available. The tourists have paid up to $35 million for the trip.

Charles Simonyi, 60, who made a fortune as Microsoft's lead software developer, is now on his second voyage to the International Space Station.

But he is expected to be the last space tourist for the foreseeable future, as all Soyuz seats have now been booked for astronauts and cosmonauts representing the 16 countries working on the $100 billion orbital outpost.

Beginning next month, the station's resident crew is due to double from three to six, all of whom will fly on Soyuz capsules.

NASA and its partners will be solely dependent on Russia for crew transport due to the retirement of the U.S. space agency's shuttle fleet next year.

<p>Eric Anderson, President and Chief Executive Officer of Space Adventures speaks to reporters during a news conference at The Explorers Club in New York, June 11, 2008.Shannon Stapleton</p>

In a conference call with reporters on Friday, Space Adventures President Eric Anderson said his company would continue to prepare people for spaceflight on the chance that seats will free up on future Soyuz missions.

There was a possibility a cosmonaut from Kazakhstan, due to fly later this year, may not make the trip, Anderson said -- although a NASA spokesman said he had not heard of any changes to the crew.

Space Adventures, based in Alexandria, Virginia, is also pursuing dedicated commercial Soyuz missions, the first of which could be ready to fly as early as 2012, Anderson said.

While Space Adventures' high-flying leisure business has been hit by the economic downturn, potential clients are still coming forward, he said.

"The kind of person who has indicated an interest in going to space is a long-term thinker," Anderson said.

"Someone who has had a life dream of going to space is not going to let an economic downturn -- even if it's a longer one than we would have hoped -- change their objective."